1. Field of the Invention
This invention relates generally to the field of servo compensation for disk storage systems, and more particularly to a feedback control system that corrects run-out error and operates as an oscillator.
2. Description of the Related Art
Modern computer systems typically include one or more disk drive systems for storing data. The disk drive systems generally store the data in circular tracks on a disk such as magnetic or optical disks. To read and/or write data from a disk, the disk drive systems employ a read/write head to write or read data to and from a specified track in the disk.
A read/write operation typically requires the disk drive system to operate in a seek mode followed by a follow mode. In the seek mode, the disk drive system locates a desired destination track and moves the head to the destination track. In the follow mode, the disk drive system adjusts the position of the head to precisely follow the destination track so that the data can be written to or read from the destination track.
During the follow mode, however, conventional disk drive systems typically encounter run-out errors. Run-out errors may occur due to various physical imperfections in the disk or the disk drive system that causes the head to be imperfectly positioned over the destination track. For example, a run-out error may occur when the disk or the circular tracks on the disk do not spin perfectly about the central axis of the disk. This condition causes a first harmonic run-out error, which is typically the same on all tracks of the disk. In addition, a second harmonic run-out condition can occur due, for example, to a warping of the disk, in which case the run-out error may be substantially different at different tracks.
FIG. 1 illustrates a schematic diagram of an exemplary disk drive system 100 for showing a run-out error. The disk drive system 100 includes a disk 102 having a circular track 104 centered about a disk center 110. A head 108 is attached to an actuator 106 for writing or reading data to and from the track 104 on the disk 102. The disk center 110 is not concentric with the spin axis 112 of the disk 102. In this arrangement, the misalignment of the disk center 110 and the spin axis 112 causes the head 108 to be positioned off the center of the track 104 as the disk 102 spins, thereby resulting in a run-out error.
In order to properly perform read and write operations on a track, the head must be following the desired track without substantial run-out errors. For instance, if the head is mis-positioned over a particular track during a write operation, data may be partially written on an adjacent track, thereby overwriting the previously written data on the adjacent track and causing catastrophic loss of the data. During a read operation on the other hand, mis-positioning of the head due to a run-out error may cause a degrade of the read back signal such that the desired data may not be read properly. Hence, the run-out error must be substantially corrected before writing or reading data to and from the desired track.
To correct run-out errors, convention disk drive systems generally employ a servo compensation system in a feedback arrangement. For example, U.S. Pat. No. 6,088,186, entitled xe2x80x9cServo Compensation Systemxe2x80x9d describes in the background, several conventional disk drive systems utilizing a servo compensation system for correcting run-out errors.
Unfortunately, however, these traditional disk drive systems and methods typically require a substantial response time to adjust the head properly over the destination track in the follow mode if the run-out conditions are not the same on all tracks. For example, a conventional disk drive system gradually adjusts the position of a head to the center of a destination track over several revolutions of the disk in a feedback loop arrangement. These extra revolutions of the disk lengthens access time of the disk drive by several folds. Since disk drive access times typically represent one of the critical paths in a computer system, such a lengthy response time to adjust to the destination track is undesirable.
Thus, what is needed is a method and a system for efficiently correcting run-out errors in disk drive systems without a substantial response time to adjust to the physical conditions of the destination track.
The present invention fills these needs by providing a method and a system that efficiently compensate for run-out errors without substantial transients and with significant improvement in response time. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, a method, or a computer readable medium.
The present invention provides a method for correcting run-out errors in a disk drive system, which includes a servo compensation system coupled to a read/write head. The servo compensation system is adapted to generate a run-out correction waveform for a track in a disk. The run-out correction waveform including one or more sinusoidal component waveforms, each of which is defined by a phase and an amplitude. The method includes measuring an amplitude and a phase of one or more sinusoidal component waveforms for a set of specified tracks in a disk. The method also includes determining a phase and an amplitude of one or more sinusoidal component waveforms for a destination track based a measured amplitude and a measured phase of the one or more measured sinusoidal component waveforms. The sinusoidal component waveforms for the destination track are adapted to substantially correct a run-out error in the destination track. The method further includes generating a run-out correction waveform for the destination track such that the disk drive system substantially corrects the run-out error in the destination track.
In another embodiment, the present invention provides a servo compensation system for correcting run-out errors in a disk drive system, which includes the servo compensation system coupled to a read/write head. The servo compensation system is adapted to generate a run-out correction waveform for a track in a disk. Each run-out correction waveform includes one or more sinusoidal component waveforms and each sinusoidal component waveform is defined by a phase and an amplitude. The system includes means for measuring an amplitude and a phase of one or more sinusoidal component waveforms for a set of specified tracks in a disk. The system also includes means for determining a phase and an amplitude of one or more sinusoidal component waveforms for a destination track based on a measured amplitude and a measured phase. The one or more sinusoidal component waveforms for the destination track are adapted to substantially correct a run-out error in the destination track. In addition, the system includes means for generating the one or more sinusoidal component waveforms for the destination track such that the disk drive system substantially corrects the run-out error in the destination track.
In yet another embodiment, a method for adjusting run-out correction waveforms in a disk drive system is disclosed. The disk drive system includes a servo compensation system coupled to a read/write head. The servo compensation system is adapted to generate sinusoidal component run-out correction waveforms, each of which is defined by a phase and an amplitude. The disk drive system operates in a seek mode from a start track to a destination track. The start track and the destination track have sinusoidal component run-out correction waveforms that are each defined by a phase and an amplitude. The method includes (a) adjusting, for each sinusoidal component run-out correction waveforms, the phase from a sinusoidal component run-out correction waveform for the start track in response to the phase adjustment value; (b) adjusting, for each sinusoidal component run-out correction waveforms, the amplitude from the start track in response to the amplitude adjustment value; and (c) generating the sinusoidal component run-out correction waveforms for the destination track such that the disk drive system substantially corrects the run-out error in the destination track.
The present invention thus provides methods and a system for efficiently correcting run-out errors in disk drive systems without a substantial response time to adjust to the physical conditions of the destination track. In addition, the present invention reduces position error signal transients after seeks by forcing the compensation system to generate a proper run-out correction waveform immediately after a seek operation. Accordingly, run-out errors are corrected substantially instantaneously at the beginning of a follow mode without a substantial response time. These and other advantages of the present invention will become apparent to those skilled in the art upon a study of the specification and drawings describing the present invention.